Telephony devices, such as telephones, analog fax machines, and data modems, have traditionally utilized circuit-switched networks to communicate. With the current state of technology, it is desirable for telephony devices to communicate over the Internet, or other packet-based networks. Heretofore, an integrated system for interfacing various telephony devices over packet-based networks has been difficult due to the different modulation schemes of the telephony devices. Accordingly, it would be advantageous to have an efficient and robust integrated system for the exchange of voice, fax data and modem data between telephony devices and packet-based networks.
An echo canceller is a device that removes the echo present in a communication signal, typically by employing a linear transversal filter. Due to non-linearities in hybrid and digital/analog loops and estimation uncertainties, linear cancellers cannot entirely remove the echo present. A non-linear device, commonly referred to as a non-linear processor (NLP), can be used to remove the remaining echo. This device may be a variable loss inserted into the system or a device that removes the entire signal and injects noise with the correct level, and possibly the correct spectrum.
A packet voice system contains many detectors that detect various parameters of the communication signal, such as voice activity levels, dual-tone multi-frequency signals, call progress tones, FAX/modem tones, etc. Because certain assumptions about the communication signal can be made based upon the state of the NLP, at times the functions of these various detectors can be unnecessary and/or redundant.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.